A piston actuator typically includes a piston disposed inside a cylinder. The piston actuator may be single-acting or double-acting. If the piston actuator is single-acting, the piton actuator may employ fluid to drive the piston in one direction, and a spring may return the piston to a fail-safe position such as, for example, a closed position or an open position. If the piston actuator is double-acting, the piston actuator may employ fluid to drive the piston in either of two directions.